Wis. Stat. § 898.30: Defense in actions by assignee.

In every action brought by the assignee of such bond the defendants shall be entitled to plead a voluntary return of the prisoner to the liberties of the jail before the commencement of such action, in mitigation thereof, as provided in s. 898.22; and to make any defense which they would be entitled to make if such action had been brought in the name and for the benefit of the sheriff to whom such bond was executed.